"It is not uncommon for injured soldiers in Iraq to be considered stable only to destabilise during transport to Germany or the United States," said Dr. Babs Soller of the University of Massachusetts Medical School. "Our device should help alert the caregiver of impending problems."

Developed by a team at the medical school, the device is a non-invasive sensor that caregivers could use to monitor oxygen and acid levels in muscles - two known indicators of circulatory shock, a life-threatening condition that can occur after a patient loses a lot of blood. Her device is based on the physiological fact that when oxygen supply decreases to a critical level, tissues start producing lactic acid. This acid production decreases the pH of the tissue, causing changes in tissue spectra, which Soller is adept at measuring. Since embarking on this project almost a decade ago, she and her colleagues have developed hardware, software and algorithms to calculate muscle pH, oxygen and hematocrit from near infrared spectra readings.

"These parameters together allow us to investigate how well oxygen is being delivered to tissue and if the available oxygen is adequate to meet the cells' energy requirements," Soller said.

"Right now the device consists of a pad that holds the sensor in place over the area of tissue or muscle that you are making the measurement from and has a long fiber optic cable that goes to the monitor," said Dr. Vic Convertino, research physiologist with the U.S. Army Institute of Surgical Research.

"Obviously all of that mass is not conducive to being on the battlefield and being carried around by a medic. I think what we would all like to see is a device that is miniaturised and lighter, to be a plug and play type thing, so that it becomes an integral part of the other medical monitors that are available, particularly in emergency vehicles during transport of the casualty," he added.